\startbuffer[DemoPage]
    \hfill
    \vfill    
    \midaligned{\bold{\pagenumber}}
    \vfill
    \hfill
\stopbuffer

\setupbodyfont[ss,30pt]
\setuplayout [margin=0pt, width=fit]
\setuppagenumbering [alternative=doublesided,location=]
\showframe
\setuplayout [location=middle,marking=on]


\setuppapersize[A9][A6,landscape]
\setuppaper[nx=3, ny=2]
\setuparranging [XY] 

\starttext
    \dorecurse{12}{\getbuffer[DemoPage]\page}
\stoptext

